The present invention relates generally to valve devices and more particularly to a valve device having a valve stem, valve body, and a bonnet, within which a valve stem holding member is provided and is adapted to establish metal-contact seals in cooperation with the body and the stem, whereby other replaceable sealing members can be rapidly and safely replaced while the valve device is in its opened state.
In general, a valve device of the type having a valve casing or valve body, a bonnet, and a valve stem has a construction wherein sealing members such as packings or O-rings are interposed between the bonnet and the valve stem and between the bonnet and the valve body. Since a sealing member of this character has a finite serviceable life, it requires periodical replacement.
This replacement has heretofore been accompanied by difficulties in certain installations of valve devices (hereinafter referred to as valves). For example, in the equipment of a nuclear power plant, the operation is continuous and is not stopped. For this reason, it is necessary that certain valves in the equipment have a construction such that their sealing members can be exchanged with the valves in their opened state and such that the exchanging of the sealing members can be carried out rapidly so as to shorten as much as possible the work time of the worker under conditions which may be conducive to radiation illness because fluids contaminated with radiation are being handled.
A typical valve device known in the prior art has a construction wherein the valve stem is held by only the bonnet, as will be hereinafter described in conjunction with a drawing. For this reason, the replacement of the sealing members with the valve in its opened state becomes very troublesome.